The present invention relates to an electrical test probe tip for use with testing instruments, and more particularly a wedge-shaped electrical test probe tip.
Integrated circuit devices (hereinafter referred to as xe2x80x9cICsxe2x80x9d) come in a wide variety of shapes and sizes depending on the function of the particular device. ICs have a set of pins, leads, or legs (hereinafter referred to as xe2x80x9cpinsxe2x80x9d) that function as a conductive path between the internal circuitry of the IC and the external circuit to which the IC is interfaced. ICs have evolved from devices with relatively large and widely spaced pins to devices with small, closely spaced pins. Pins on modern ICs may be spaced less than a millimeter apart.
To measure an electrical signal of an IC, a test probe is connected to an oscilloscope, digital multimeter, or other measuring, monitoring, diagnostic, or signal processing instrument (herein referred to as a xe2x80x9ctesting instrumentxe2x80x9d). At one end of a test probe is a probe tip. The probe tip may be integral or replaceable. Typically, the probe tip is an elongate conductive member that terminates in a conical, blunt, or rounded point. FIG. 1 shows one example of a traditional probe tip.
When a probe tip contacts a pin, it forms an electrical connection therewith. The electrical signal on the pin may then be measured. It is difficult to form a contact with a single pin on a modern IC using a traditional probe tip because of the small geometry and close spacing of the pins. If the probe tip contacts two adjacent pins simultaneously, a short circuit between the two adjacent pins results. A short circuit prevents measurement of the desired signal, and in some situations, may result in damage to the internal circuitry of the IC. A traditional probe tip provides no means of preventing the occurrence of a short circuit.
U.S. Pat. No. 4,943,768 to Niki, et al. sets forth a description of a testing device (hereinafter referred to as the xe2x80x9cNiki devicexe2x80x9d) for electrical circuit boards. The Niki device is designed to make simultaneous electrical connections with multiple horizontal test terminals on a circuit board and is, therefore, relatively wide. Strips of conductive material appear on the surface of the body and are arranged in conformity with the parallel test terminals on the circuit board. The Niki device has a tapered, sharp edge at its lower end that is suitable only for measurement of signals appearing on the multiple horizontal test terminals. The Niki device is unsuitable for insertion between the pins of an IC because its relatively wide body would likely contact other components on a circuit board. If the Niki device were to be inserted between adjacent pins of an IC, the result would depend on the particular arrangement of the strips of conductive material on the surface of the body. One possibility is that a strip would contact both adjacent pins causing a short circuit. A second possibility is that only the probe body would contact the pins resulting in an open circuit between the conductive strip and the testing instrument. For this reason, proper measurement of the desired signal is unlikely.
U.S. Pat. No. 4,987,364 to Watts sets forth a description of a device (hereinafter referred to as the xe2x80x9cWatts devicexe2x80x9d) for use in testing printed circuit boards. The Watts device is designed to measure signals from two types of test pads on the surface of a circuit board. The first type of test pad has a small geometry, while the second type has a large geometry with a hole in its center. The Watts device consists of a probe body that is generally thin and sheet-like (described in the specification as xe2x80x9claminarxe2x80x9d). The preferred embodiment of the Watts device has a probe body that includes a bottom edge that tapers downward in a stair-step fashion to provide a contact portion. The Watts device relies on the thin geometry of its probe body to avoid simultaneous contact with more than a single test pad. For its stated purpose, insulated surfaces on the body perpendicular to the plane of the circuit are unnecessary. Without insulated surfaces, however, insertion of the Watts device between adjacent pins of an IC would likely result in a short circuit.
U.S. Pat. No. 5,923,177 to Wardell sets forth a description of a device (hereinafter referred to as the xe2x80x9cWardell devicexe2x80x9d) for use in testing ICs. The Wardell device consists of a plurality of probe tips arranged in a row, and attached to a housing. The stated purpose of the device is to sample a plurality of pins simultaneously. Each probe tip is an elongate, relatively narrow member that is approximately the same thickness as the horizontal distance between adjacent pins of an IC. Each probe tip tapers in both thickness and width, and terminates in a flat surface perpendicular to its length. On the side of each probe tip is a conductive surface. The conductive surfaces on either side of a probe tip are not connected electrically, and are separated by alternating layers of filler material and adhesive. In contrast, the exterior conductive surfaces of two adjacent probe tips that face each other are electrically connected. The two conductive surfaces that face each other contact and sample the signal on the solitary pin that fills the space between the two probe tips. Because the Wardell device has two relatively large conductive surfaces, it is likely that the inductance of the device will be significantly larger than that of a probe tip with a single, relatively small surface. In addition, the Wardell device is not intended to directly sample the signal on a single pin. To sample the signal on a single pin the Wardell device requires that signals on the remaining pins be disregarded. Because of its laminar structure and multiplicity of probe heads, the Wardell device would be relatively expensive and complex to produce.
An electrical test probe wedge tip according to the present invention includes an electrically conductive interior optionally surrounded, at least partially, by an electrically insulated exterior surface. A longitudinal axis extends the length of the electrical test probe tip. In one preferred embodiment the top tip end has a single planar surface at an angle to the longitudinal axis.
A method of fabricating an electrical test probe tip includes providing an elongate electrically conductive blank coated with insulation. An angled surface is exposed by removing a portion of the first end along a plane at an angle to the longitudinal axis of the blank.